Torpedo nose and sonar dome construction



March 12, 1968 R. NISEWANGER 3,372,662

TORPEDO NOSE AND SONAR DOME CONSTRUCTION Filed April s, 1965 2 Sheets-Sheet 1 INVENTOR. CARROL R. NISEWANGER V. C. MU LL E R AT TOR N E Y.

March 12, 1968 1 c. R. NISEWANGER 3,372,662

TORPEDO NOSE AND SONAR DOME CONSTRUCTION Filed April 8, 1965 2 Sheets-Sheet 2 FIG. 5.

DISTANCE FROM NOSE TIP x/ Lllllllll I 28 a, INVENTOR.

CARROL R. NISEWANGER FIG. 6.

V. C. M U L LER ATTOR NE Y.

United States Patent 3,372,662 TORPEDO NOSE AND SONAR DOME CONSTRUCTION Carrol R. Nisewanger, Arcadia, Califi, assignor to the United States of America as represented by the Secretary of the Navy Continuation of application Ser. No. 446,749, Apr. 8 1965. This application Jan. 27, 1967, Ser. No. 613,069

2 Claims. (Cl. 11420) ABSTRACT OF THE DISCLOSURE A wall construction for a sonar dome or a torpedo nose is of a bonded sandwich type consisting of inner and outer face sheets of impervious impregnated fiberglass laminae, and a honeycomb core therebetween. The walls of the honeycomb are made of pervious woven fiberglass, which is partially impregnated for stiffness. Several nipples extend through the inner face sheet of the bonded sandwich construction. A vacuum is drawn throughout the honeycomb core zone through the nipples. A liquid medium for providing an acoustic match is then introduced into the honeycomb core zone under influence of the vacuum, through the nipples.

filed Apr. 8, 1965, and now abandoned.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to improved construction materials for use in making underwater, acoustically transparent, dome structures. Such dome structures are typically used to cover the transducer units of surface vessel or submarine carried sonars, or to cover the transducer unit of an acoustic torpedo, and in such applications are sometimes referred to as sonar domes. The invention also relates to an improved acoustic torpedo of the type containing its transducer unit within its pressure hull.

In instances in which sonar domes are carried by moving water vehicles, the ambient flow adjacent the outer surface of the dome wall generates flow noises in the input of the enclosed transducer. Also, vehicle body vibration noises are coupled to the dome through its supporting structure, and this vibration generates noise in the transducer. As the result of an exhaustive experimental investigation, it has been found that these flow and body vibration noises can seriously interfere with the sensitivity of the associated acoustic equipment.

On the other hand, the known prior art construction materials used in making dome walls have, without exception, been developed solely with concern for reducing transmission losses and angular distortion in the passage of acoustic signals through the wall. These prior art construction materials include plain laminated fiberglass, metals, rubber, and plastic materials. It was found that these materials result in an undesirably high ratio of flow and body vibration noise to signal, and therefore they have been deemed inadequate for use with newer more sensitive acoustic detection apparatus. The presence of flow and body vibration noises in connection with prior art sonar dome structures has, therefore, been a serious problem prior to the present invention.

Along with the aforementioned flow and vibration noise problem, the trend toward deeper operation of submarines and torpedoes raises the additional requirement that the sonar dome walls have the structural strength necessary to resist the pressures found at these depths.

Accordingly, the objectives of thepresent invention include provision of:

(1) A novel construction material, for use in making underwater, acoustically transparent, dome structures, and which has flow and body vibration noise damping properties.

(2) A construction material in accordance with the previous objective having the structural strength necessary for the resistance of the pressures found at the operating depths of modern torpedoes and submarines.

(3) An improved acoustic torpedo of the type containing its transducer unit within its pressure hull, and which provides a lower ratio of flow and vibration noise to signal at the input of the transducer than obtainable with prior art apparatuses.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a longitudinal section through a nose portion of an acoustic torpedo constructed in accordance with the present invention;

FIG. 2 is an enlarged detail of a zone 2-2 of FIG. 1, and which also is a section taken along line 22, FIG. 3;

FIG. 3 is a section taken along line 3-3, FIG. 2;

FIG. 4 is a section, similar to FIG. 3, illustrating a modification of the invention;

FIG. 5 is an idealized graphical plot of pressure distribution along the surface of the hull of the torpedo of FIG. 1; and

FIG. 6 illustrates an alternate form of invention.

Referring now to the drawing, and more particularly to FIG. 1, there is illustrated a portion 10 of a torpedo adjoining its front end, and which includes that portion of the hull which forms the torpedos hydrodynamic nose. Axis A is the torpedos longitudinal axis and reference plane B is a transverse plane through the torpedo at the point along its hull where the hydrodynamic nose merges with a cylindrical hull surface extending rearwardly therefrom. The specific nose shape shown, is that of one half of an ellipsoidal body of revolution having a 2:1 length to width ratio about its major axis. The distance C, from the tip of the nose to reference plane B corresponds to one half of the length of the major axis of the ellipsoid, and the torpedo diameter'D, at reference plane B corresponds to length of its minor axis. Portion 10 of the torpedo comprises separately formed hull sections 12 and 14. Section 12 forms the sonar dome and compartment for containing the torpedos transducer unit, and section 14 forms a compartment for containing an explosive warhead, electronic equipment, or the like (not shown). The remaining portion of the torpedo extending aft from portion 10 may be of any suitable construction and includes the torpedo propulsion power plant and the propulsion mechanism (not shown).

Transducer dome section 12 comprises a shell 16 of honeycomb reinforced, fiberglass material, which will hereinafter be described in detail. An internal annular flange 18 is bonded to the rear marginal edge of shell 16, and a plate or bulkhead 20 is secured to flange 18 by a plurality of angularly spacer screws. Bulkhead 20 closes the rear end of shell 16 forming a closed chamber 22. Disposed in chamber 22 is a transducer unit 24. Unit 24 is fixedly attached to bulkhead 20 by means of a support tube 26. The void space in chamber 22 is filled with an acoustic impedance matching liquid 28, such as deaerated and'deionized distilled water.

Transducer unit 24, which is conventional and per se forms no part of the invention, is of a type providing an acoustic beam pattern which extends to either side of axis A, in bearing, in order to give the torpedos acoustic detection apparatus a side looking capacity to sense laterally disposed targets. Unit 24 is formed as a half-barrel or semi-cylindrical structure about a vertical axis E, with the end faces of individual transducer elements arranged in vertical staves or rows 30 angularly spaced about its semi-cylindrical face. Electrical connections to unit 24, not shown, communicate with the compartment within the adjacent hull section 14 through the support tube 26.

Referring again to FIG. 1, but this time also in conjunction with FIGS. 2 and 3, shell 16 comprises a bonded sandwich construction consisting of inner and outer face sheets or laminae 32 and 34, and a honeycomb core 36 disposed therebetween. The inner and outer face sheets 32, 34, are made of fiberglass fabric, which has been thoroughly impregnated with epoxy resin, and therefore is non-porous and stiff. Honeycomb core 36 is made of fiberglass fabric, which is only partially impregnated with epoxy resin so that it is stiff, but retains the inherent porosity of the Woven fabric to permit communication of liquids between the honeycomb cells. In FIGS. 2 and 3, the cross section of non-porous material is represented by diagonal cross hatching consisting of alternate unbroken thick lines and unbroken thin lines, and the cross section of porous material is represented by diagonal cross hatching consisting of alternate unbroken thick lines and broken thin lines. As best shown in FIG. 3, the honeycomb core 36 is formed from alternately disposed serpentine strips 38 and straight strips 40. A preferred material is the commercially available multiwave cellular core material in which the basic strips 38 and 40 themselves have a small serpentine wave structure. This alternate serpentine and straight strip core construction has been found to be particularly convenient for use in forming the previously described ellipsoidal nose shape, with its inherent high degree of curvature at the nose. Sectors formed of this alternate serpentine and straight strip construction and with the strips generally aligned in the longitudinal direction of the torpedo, have been found convenient to handle in laying up the bonded sandwich construction, over the ellipsoidal mandrel or form, as will be understood by those familiar with the art of fabricating contoured structures from laminated sheets of plastic type materials. The marginal portion at the rear end of shell 16 is formed as a laminated band 42, also of impregnated fiberglass. Band 42 serves as a reinforcing element, and internal flange 18 is in part bonded to the sandwich shell construction, and in part bonded to band 42. Another band 44 of laminated cnstruction, is bonded to the interior of the shell adjacent the front end of flange 18. The flange 18, and bands 42 and 44 together form an exceptionally rigid and high strength scheme of bonded joints at the rear end of shell. One or more threaded openings 46 are formed in and through band 44 and the adjacent inner sheet 32, and a suitable pipe coupling element 48 is threaded into opening 46 to provide communication with the porous honeycomb core 36 in shell 16. The honeycomb cells and other voids in porous honeycomb core 36 are filled with the acoustic impedance matching liquid 28 through a nipple or pipe coupling elements 48, prior to final assembly of a torpedo for use. This may be conveniently done by a suitable system of check halves and manifold connections for first drawing a vacuum throughout the porous honeycomb core 36, and then allowing the liquid 28 to be drawn into the honeycomb by the vacuum therein. The outer surface of outer facing sheet 34 is polished to insure good hydrodynamic qualities. As an alternative to the serpentine and straight strip form of honeycomb, the core of shell 16 may be made of hexagonal form of honeycomb 50, FIG. 4. As an alternative to liquid 28, the cellular core may be filled with any other suitable viscous medium, such as a jell.

Hull section 14 has a metal shell 52, which for a short linear portion thereof adjoining its front end, is shaped to form part of the ellipsoidal nose, whereby no interruptions in the contour of the torpedo body are created. An integral annular flange 54 is formed at the front end of shell 52. The transducer compartment section 12 and the adjacent section 14 are detachably secured together by an acoustic vibration isolation joint which comprises the confronting surfaces of bulkhead 20 and internal annular flange 54, a retainer ring 56, and gaskets 58 and 60 of rubber or rubber-like materials. These members are secured together by a plurality of angularly spaced cap screws 61 which extend through apertures through retainer ring 56, flange 54, and gaskets 58 and 60, with the ends of the screws threaded into tapped holes in bulkhead 20. The gaskets 58 and 60 are disposed between the confronting surfaces of bulkhead 20 andflange 54, and the confronting surfaces of flange 54 and retainer ring 56, respectively. And, the apertures through flange portion 54 are oversized and contain rubber grommets 62. Provision of these gaskets and grommets prevents any metal to metal contact in the attachment of the hull sections 12 and 14.

Referring now to the graphical plot shown in FIG. 5, curve 64 represents the idealize pressure distribution along the outer surface of hull portion 10, under forward motion of the torpedo. This pressure distribution is the result of the previously described ellipsoidal nose shape. The plot is taken from page 42 of Cavitation and Pressure Distribution, (Studies in Engineering Bulletin 32.), by Hunter Rouse and John S. McNown, published by Iowa State University Institute of Hydraulic Research, 1948. It is to be noted that the geometry of hull sections 12 and 14 are such that the isolation joint between them is disposed at a distance equal to 0.7 C. from the tip of the nose, which corresponds to the axial distance for the minimum value of curve 64-, and that pressure distribution ahead of this minimum value continuously decreases in the rearward direction. In accordance with conventional principles of hydrodynamic design, the flow adjacent the portion of the hull ahead of such location tends to remain laminar, with transition to turbulent flow occurring aft of such location. It will be apparent, therefore, that location of the isolation joint is chosen to be ahead of the transition to effectively isolate transducer compartment section 12 from flow noise due to turbulent flow along the hull. Machinery vibrations coming from propulsion machinery located in the rear portions of the torpedo body are also isolated from the transducer compartment by this isolation joint.

Exhaustive tests have proven that the described torpedo construction is particularly advantageous in that it results in a substantially lower flow and hull vibration noise to signal ratio than has been observed in connection with any of the tested prior art constructions. At the same time, shell 16 has been found to have excellent properties for use as an acoustically transparent wall medium, i.e. low losses and little distortion of signal. The honeycomb reinforced construction of shell 16 also providesa high degree of strength for resistance to the high pressures encountered at the deep depths of operation of the newer antisubrnarine torpedoes.

A feature of the invention believed particularly important, is the bonded sandwich construction of shell 16, and the filling of its porous honeycomb core with a liquid or other viscous medium. The various test results indicate that this dome wall construction has vibration damping qualities. The epoxy resin which is used for impregnating the fiberglass fabric and as the adhesive agent for bonding the sandwich structure together is known to have a property of forming structural joints which are capable of absorbing the structural vibration imparted to the joint. It is believed that the use of such an adhesive agent in the fabrication of the shell, and the filling of the cells and other voids of the honeycomb with a liquid medium are both factors which enhance damping of the vibrations. Vibration is also inhibited by the high degree of stiffness inherent to the honeycomb'reinforced form of construction. While epoxy resin demonstrated itself to have excellent properties as an impregnation and adhesive agent, it is expected that other adhesives of the type known to have similar properties will produce the same good results.

FIG. 6 illustrates a general application of the porous honeycomb reinforced wall construction in connection with a tear drop shaped sonar dome 66 mounted to the bottom of a surface ship 68. Wall 16A of the dome is made of the same structure as the shell of the transducer compartment in FIG. 1, and is similarly filled with an acoustic impedance matching liquid medium 28A. Shell 16A forms a chamber containing the sonar transducer unit 24A immersed in liquid medium 28 A. Unit 24A is of the barrel type having a full 360 cylindrical surface containing vertical staves of transducer faces. The flange and joint structure 70, by which shell 16A is mounted to the ship =68, is preferably of an acoustic vibration isolation type.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A method for making an acoustically transparent torpedo nose wall, comprising the steps of:

(l) laying up an inner layer of impervious material upon an ellipsoidal form, said inner layer being provided with at least one nipple adapted to be separably connected to a vacuum line, said nipple extending through said inner layer and accessible from the inside of the nose wall,

(2) laying up and bondingly joining an intermedial layer of pervious honeycombed cellular material over said inner layer,

(8) the intermediate layer of pervious honeycomb material has the walls of the cells thereof formed of woven glass fabric partially impregnated with plastic, but only to a degree by which they remain pervious to the liquid.

References Cited UNITED STATES PATENTS 3,123,176 3/1964 Greenberg 181-.5 3,136,380 '6/1964 McCoy et a1. 18I-.5 3,139,056 6/1964 Boswell et al. 11422 BENJAMIN A. BORCHELT, Primary Examiner. P. A. SHANLEY, W. KUJAWA, Assistant Examiners. 

